Reprinted  from  Journal  of  Bacteriology 
Vol.  IV,  No.  4,  July,  1919 


A SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP  OF 

BACTERIA 

JOHN  J.  WENNER  and  LEO  F.  RETTGER 

From  the  Sheffield  Laboratory  of  Bacteriology  and  Hygiene,  Yale  University 
Received  for  publication  March  8, 1919 

The  term  Proteus  signifies  changeability  of  form,  as  personi- 
fied in  the  Homeric  poems  in  Proteus,  “the  old  man  of  the  sea,” 
who  tends  the  sealflocks  of  Poseidon  and  has  the  gift  of  endless 
transformation.  The  first  use  of  this  term  in  bacteriological 
nomenclature  was  made  by  Hauser  (1885)  who  described  under 
this  term  three  types  of  organisms  which  he  isolated  from  putrefied 
meat.  Variations  in  form  and  size  and  in  cultural  characters 
were  the  basis  of  his  classification.  Other  investigators  have 
since  applied  the  name  Proteus  to  specific  organisms  which  they 
isolated  from  various  sources.  Of  these  organisms  some  show 
close  similarities  and  in  many  instances  are  identical  with  the 
types  described  by  Hauser.  Some  do  not  appear,  however, 
to  have  sufficient  common  properties  to  justify  inclusion  in  the 
Proteus  group,  and  attempts  to  place  them  here  tend  to  further 
obscure  the  poorly  defined  limits  of  this  group. 

The  three  species  which  Hauser  described  under  the  genus 
Proteus  were  as  follows : Proteus  vulgaris , which  liquefied  gelatin 
and  formed  zooglea  in  this  medium,  and  which  was  very  active 
in  its  various  physiological  properties;  Proteus  mirahilis  which 
likewise  liquefied  gelatin  and  formed  zooglea,  but  which  was 
less  active;  and  Proteus  zenkeri,  which  was  unable  to  liquefy 
gelatin  and  which  was  relatively  inactive.  The  main  basis  for 
distinguishing  the  three  species  appears  to  be  their  action  on 
gelatin. 

Babes  (1889)  isolated  an  organism  from  a case  of  lung  gan- 
grene in  man  which  he  called  Proteus  lethalis,  and  another  from  the 

331 


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JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


organs  of  a child  which  died  with  symptoms  of  septicemia,  Pro - 
tend  septicus.  The  same  bacterium  was  later  described  by 
Kruse  (1896).  These  organisms  appear  to  be  very  closely  re- 
lated to  one  or  two  of  Hauser’s  types,  if  indeed  they  are  not  identi- 
cal with  them. 

Jaeger  (1892)  isolated  a fluorescent  organism  which,  due  to 
some  points  of  similarity  with  the  Proteus  group,  he  called  Pro- 
teus fluoresecens.  It  was  described  as  the  causative  factor  in 
several  cases  of  Weil’s  disease.  It  has  since  been  isolated  from 
similar  cases  by  Bar  and  Renon  (1895),  by  Conradi  and  Vogt 
(1901),  and  by  Bruning  (1904).  While  this  organism  in  a general 
way  bears  some  resemblance  to  the  Proteus  group,  it  is  so  atypi- 
cal that  its  inclusion  in  this  division  may  be  seriously  ques- 
tioned. A more  natural  grouping  would  place  it  in  the  genus 
Pseudomonas. 

Fuller  and  Johnson  (1899)  describe  two  spore-forming  organ- 
isms as  Proteus.  The  property  of  forming  proteus-like  colonies 
on  gelatin  seems  to  be  their  sole  basis  of  classification,  hence  these 
organisms  may  be  eliminated  from  further  consideration,  especi- 
ally because  no  other  spore-producing  bacteria  have  been  re- 
ferred to  the  Proteus  group. 

Prior  to  the  work  of  Hauser  an  organism  was  described  by 
Kurth  (1883)  which  on  account  of  its  marked  resemblance  to 
Hauser’s  Proteus  zenkeri  deserves  mention  here.  Kurth’s  Bac- 
terium zopfii  was  isolated  from  the  intestine  of  fowls,  and  has 
since  been  observed  by  others  on  numerous  occasions. 

The  purpose  of  the  present  investigation  was  to  determine 
the  exact  relation  of  the  Proteus  group  to  other  groups  of  organ- 
isms, and  to  point  out  more  clearly  than  has  been  done  hereto- 
fore the  specific  properties  which  serve  to  distinguish  the  members 
of  what  has  so  generally  been  termed  the  u Proteus  group.” 

For  this  purpose  84  strains  were  obtained  from  different 
sources.  Of  these  58  were  procured  from  other  laboratories, 
and  were  labelled  as  follows: 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


333 


B.  proteus-vulgaris 27 

B.  proteus-mirabilis 8 

B.  proteus-zenkeri 4 

B.  proteus 13 

B.  zopfii 5 

B.  proteus-viridis 1 


Twenty-six  different  strains  were  isolated  in  this  laboratory, 
of  which  25  were  of  the  Proteus  vulgaris  or  Proteus  mirabilis , and 
one  of  the  B.  zopfii  or  Proteus  zenkeri  type. 

A morphological  and  cultural  study  of  the  organisms  of  this 
collection  showed  that  it  could  be  divided  into  the  three  fol- 
lowing divisions: 

Group  I comprising  Proteus  vulgaris s Proteus  mirabilis,  and 
Bacillus  proteus. 

Group  II  comprising  Proteus  zenkeri  and  Bacterium  zopfii. 

Group  III  comprising  Proteus  fluorescens. 

The  members  of  group  I are  Gram  negative  and  very  actively 
motile,  and  on  agar  show  a peculiar  spreading  growth.  They 
usually  exert  proteolytic  action  on  gelatin  and  in  milk,  and  to 
some  extent  attack  carbohydrates,  and  protein  material  in 
general.  Furthermore,  they  grow  luxuriantly  on  all  of  the  ordi- 
nary media,  and  are  not  limited  to  any  specific  temperature 
range. 

The  two  types  which  comprise  group  II  are  distinctly  Gram- 
positive. They  possess  no  proteolytic  action  and  do  not  attack 
carbohydrates;  neither  do  they  produce  a luxuriant  spreading 
growth  on  moist  agar,  as  do  the  members  of  group  I.  They 
develop  very  poorly  in  liquid  media. 

The  one  available  strain  of  group  III  differed  markedly  from 
the  organisms  of  the  other  two  groups.  Fluorescent  pigment  pro- 
duction, together  with  its  other  properties  so  characteristic  of 
the  fluorescent  group,  should  naturally  place  this  strain  within 
the  genus  Pseudomonas. 

While  Hauser  at  first  described  the  Proteus  group  as  being  com- 
posed of  three  distinct  species,  that  is  P.  vulgaris,  P.  mirabilis, 
and  P.  zenkeri,  he  later  thought  that  the  last  two  species  might 
be  only  varieties  of  Proteus  vulgaris.  His  latter  conclusion  seems 
to  have  been  accepted  by  most  investigators,  though  little  evi- 


JOURNAL  OF  BACTERIOLOGY,  VOL.  IV,  NO.  4 


334 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


dence  can  be  found  to  substantiate  it.  Kendall  (1916)  states 
“that  it  is  now  recognized  that  cultures  of  B.  proteus  may  grad- 
ually lose  their  gelatin-liquefying  power  after  prolonged  cultiva- 
tion, so  that  a cultural  transition  from  B.  proteus  to  B.  zenkeri 
may  be  observed  in  the  laboratory.”  While  we  have  observed 
loss  of  ability  to  liquefy  gelatin  in  certain  strains,  we  have  never 
noted  other  changes  in  Proteus  vulgaris  which  would  tend  to 
give  it  the  characters  of  Proteus  zenkeri. 

In  the  present  study  the  strains  of  Proteus  which  were  labelled 
Proteus  vulgaris  and  Proteus  mirabilis  when  received  were  found 
to  be  practically  identical  in  all  of  their  characters.  Both  liq- 
uefied gelatin  with  the  same  rapidity.  Although  in  each  species 
variability  in  proteolytic  action  was  noted  in  a few  instances,  no 
other  changes  accompanied  the  partial  or  complete  loss  of  gela- 
latin-liquefying  power,  and  the  strains  did  not  in  the  least  assume 
the  characters  of  Hauser’s  Proteus  zenkeri.  Thus  it  appears 
that  the  classification  of  Hauser  holds  only  in  so  far  as  the  separa- 
tion of  his  species  Proteus  zenkeri  from  the  other  two  is  concerned. 

Kruse  (1896)  and  Chester  (1909)  noted  a similarity  between 
Hauser’s  Proteus  zenkeri  and  Bacillus  zopfii  of  Kurth  (1883). 
We  have  found  the  two  to  be  identical,  and  hence  would  classify 
them  as  one  and  the  same  genus  under  the  generic  name  of 
Zopfius. 

The  types  which  were  labelled  Proteus  vulgaris , Proteus  mira- 
bilis and  Bacillus  proteus  have  been  reduced  by  us  to  two  species, 
namely  Proteus  vulgaris  and  Proteus  mirabilis , as  B.  proteus  is 
but  another  name  applied  to  either  or  both  of  the  others.  The 
Proteus  group  as  a whole  is  sometimes  referred  to  as  Bacillus 
proteus;  but  the  use  of  this  name  should  be  discontinued. 

In  the  present  investigation  the  original  Proteus  group  of 
Hauser  has  been  split,  therefore,  into  two  distinct  genera,  namely 
Proteus  and  Zopfius.  In  the  former  are  included  P.  vulgaris  and 
P.  mirabilis  of  Hauser,  together  with  the  strains  in  our  collection 
labelled  Bacillus  proteus , and  under  the  genus  Zopfius , Bacterium 
zopfii  of  Kurth  and  Proteus  zenkeri  of  Hauser.  The  basis  for 
this  classification  will  be  brought  out  further  in  the  data  and 
discussions  which  follow. 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


335 


GENUS  PROTEUS 

This  genus  may  be  defined  as  comprising  organisms  which  in 
form  are  small  coli-like  rods  with  rounded  ends  and  occurring 
singly,  in  pairs  or  in  chains;  they  are  Gram  negative,  form  neither 
spores  not  capsules,  and  are  actively  motile  by  means  of  peri- 
trichiate  flagella.  Gelatin  is  usually  liquefied  rapidly,  though 
this  property  may  be  entirely  lost.  When  inoculated  into  the 
condensation  fluid  of  slant  agar  tubes  a rapidly  spreading  growth 
is  produced  over  the  entire  surface  of  the  agar.  The  strains 
ferment,  with  acid  and  gas  production,  glucose,  levulose,  galac- 
tose, sucrose  and  glycerol  and  occasionally  maltose.  Alkalinity 
is  usually  produced  in  litmus  milk,  followed  by  decoloration  of 
the  litmus  and  digestion  of  the  casein.  At  times  there  is  slight 
coagulation  or  precipitation  of  casein  with  subsequent  re-solu- 
tion or  digestion. 

Organisms  of  this  genus  are  widely  distributed  in  nature,  and 
have  been  isolated  from  numerous  sources.  Their  presence  in 
soil  appears  to  depend  largely  upon  recent  contamination  with 
animal  excreta  or  putrefactive  organic  matter  of  animal  origin. 
Cantu  (1911)  was  able  to  isolate  organisms  of  this  genus  from 
23  out  of  52  samples  of  garden  soil. 

Members  of  this  genus  are  often  present  in  stagnant  pools, 
sluggish  streams  and  other  contaminated  waters.  We  have 
obtained  them  from  stagnant  pools,  aquaria  and  street  washings. 
Ward  (1899)  isolated  several  strains  from  the  Thames  River, 
and  Jordan  (1903)  from  the  waters  of  the  upper  Mississippi. 
Horowitz  (1916)  made  several  isolations  from  snow  water. 

Proteus  organisms  may  be  said  to  be  present  in  practically  all 
sewage,  for  here  there  is  a constant  source  of  contamination  and 
a favorable  medium  for  development. 

The  presence  of  this  genus  in  the  intestinal  tract  of  man  is 
by  many  authorities  regarded  as  an  indication  of  intestinal 
trouble  or  some  other  pathological  condition.  Ford  (1901) 
claims  to  have  isolated  it  from  various  parts  of  the  intestine, 
but  as  some  of  his  organisms  were  fermenters  of  lactose,  there  is 
some  doubt  as  to  whether  all  were  Proteus.  Stewart  (1917)  be- 


336 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


lieves  that  Proteus  members  found  in  war  wounds  are  of  non- 
fecal  origin.  In  the  examination  of  several  thousand  samples 
of  feces  from  dysentery  convalescents  he  found  this  genus  to  be  a 
very  uncommon  inhabitant  of  the  colon  of  man.  It  may  be 
obtained  from  the  intestinal  tract  of  lower  animals,  as  for  example 
guinea  pigs.  Jensen  (1903)  observed  this  genus  to  be  present 
in  large  numbers  in  calves  affected  with  a form  of  dysentery. 
Its  presence  in  similar  conditions  in  man  and  animals  may  in 
part  account  for  its  wide  distribution  in  nature. 

The  most  favorable  habitat  of  the  genus  Proteus  is  decompos- 
ing organic  matter  of  animal  origin.  In  such  material  it  is  almost 
invariably  present.  Cantu  (1911)  was  able  at  will  to  isolate  it 
from  putrefied  meat,  as  have  many  other  investigators.  Wyss 
(1898)  obtained  a strain  of  Proteus  from  dead  fish,  and  Shrank 
(1888)  from  spoiled  eggs.  Isolations  have  been  made  also  from 
human  cadavers,  where  this  organism  was  found  in  large  numbers 
by  Hauser  (1885),  Hofmeister  (1893),  Haegler  (1892)  and  Kuhn 
(1891).  We  were  able  to  obtain  it  from  meat  which  had  been 
allowed  to  undergo  decomposition,  and  from  the  partly  decom- 
posed bodies  of  dead  rabbits  and  guinea-pigs. 

Method  of  isolation 

Until  quite  recently  the  usual  gelatin  and  agar  plate  methods  of 
solation  have  been  employed  for  this  group.  As  these  were  very 
faulty  for  this  type  of  bacteria,  many  efforts  resulted  in  failure. 
The  newer  methods  have  rendered  valuable  service,  however.  In 
the  present  work  the  procedure  of  Cantu  (1911)  was  at  first 
adopted.  Gelatin  tubes  are  inoculated  directly  with  the  mate- 
rial in  question.  After  incubation  at  20°C.  for  several  days 
transfers  are  made  from  tubes  in  which  liquefaction  has  taken 
place  to  the  condensation  fluid  of  new  slant  agar  tubes.  If 
Proteus  organisms  are  present  a rapidly  spreading  growth  occurs 
in  twelve  to  twenty-four  hours  at  30°  to  37  °C.  This  growth  is 
quite  characteristic  and  usually  spreads  over  the  entire  surface. 
From  the  uppermost  portion  of  the  surface  growth  inoculations 
are  made  in  the  condensation  fluid  of  a second  agar  tube,  and 
the  process  repeated  until  a pure  culture  is  obtained. 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


337 


It  soon  became  apparent  in  the  present  investigation  that  the 
materials  for  study  could  be  inoculated  directly  into  the  condensa- 
tion water  of  the  sloped  agar  tube,  and  the  period  in  which  isola- 
tion is  effected  very  much  shortened.  This  modification  in  no 
way  detracts  from  the  merits  of  the  Cantu  procedure.  As  a 
rule  very  little  effort  is  required  to  effect  complete  isolation  of 
the  Proteus  genus,  owing  to  its  peculiar  property  of  overspread- 
ing agar  rapidly  and  leaving  associated  organisms  behind  in  the 
condensation  fluid.  Fresh  agar  is  necessary,  however,  and  the 
results  are  greatly  facilitated  by  washing  the  agar  surface  with 
the  condensation  water  just  before  inoculation. 

General  characters  of  the  Genus  Proteus 

The  salient  features  of  this  genus  have  already  been  defined. 
The  following  is  an  elaboration  of  the  different  characters,  in  so 
far  as  Journal  space  will  permit.1 

The  individual  cells  are  usually  short  Coli-like  rods  with 
rounded  ends,  varying  in  dimensions  from  0.4  to  0.6/*  by  1.2  to 
2.5/*,  though  occasionally  much  longer  cells  are  seen.  The  rods 
may  be  grouped  singly,  in  pairs  or  in  short  chains.  They  are 
actively  motile,  possessing  peritrichous  flagella.  The  unstained 
cells  appear  homogeneous  in  structure.  Neither  spores  nor 
capsules  have  been  observed.  All  strains  are  at  all  times  Gram- 
negative. Young  cultures  are  readily  stained  with  methylene 
blue,  fuchsin  and  other  common  basic  dyes. 

Members  of  the  Proteus  genus  grow  luxuriantly  on  the  usual 
solid  and  liquid  laboratory  media.  They  are  capable  of  grow- 
ing within  a wide  range  of  temperature,  and  within  reasonable 
limits  development  is  not  materially  affected  by  change  in  hydro- 
gen ion  concentration. 

Various  ranges  of  temperature  have  been  reported  as  most  favor- 
able. Hauser  (1885)  gives  20°  to  34°C.  as  the  optimum.  Kendall 
(1916)  places  it  at  about  25°.  Berthelot  (1914),  Cantu  (1911), 
and  Glenn  (1911)  grew  the  organisms  successfully  at  37°.  Levy 

xFor  more  complete  descriptions  and  discussions  the  reader  is  referred  to  the 
doctorate  thesis  (J.  J.  Wenner)  in  the  Yale  University  Library. 


338 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


(1894)  showed  that  the  group  develops  slowly  at  a temperature 
as  low  as  0°  and  as  high  as  43°  to  45°C.  We  have  invariably 
obtained  maximum  growth  at  34°  to  37°.  Good  growth  was 
obtained  also  at  20°,  though  longer  incubation  was  required,  as 
shown  for  example  in  glucose  broth  culture  in  which  maximum 
acidity  was  attained  in  twenty-four  hours  at  37°,  as  against  forty- 
eight  hours  at  20°,  and  maximum  gas  production  in  twenty-four 
hours  at  37°,  as  against  one  hundred  and  twenty  hours  at  20 °C. 

Growth  on  plain  agar 

The  most  characteristic  growth  of  Proteus  is  obtained  on  slant 
agar.  This  was  pointed  out  by  Cantu  (1911)  when  he  showed 
that  inoculation  in  the  condensation  fluid  of  fresh  sloped  agar 
resulted  in  a uniform  growth  over  the  entire  surface.  This 
growth  may  be  homogeneous,  or  of  a more  or  less  peculiarly 
modeled  character.  It  is  of  a butyrous  consistency.  If  the 
surface  of  the  inoculated  agar  is  dry  a streak  inoculation  results 
in  a pronounced  growth  which  spreads  very  irregularly,  with  a 
more  or  less  lacerated  margin.  The  extent  of  the  spreading 
depends  on  the  amount  of  moisture  on  the  agar. 

Colony  growth  on  plate  agar  may  be  at  times  characteristic, 
that  is,  of  ameboid  appearance,  or  in  the  form  of  large  colonies 
which  are  more  or  less  rosette-like,  with  very  irregular  borders. 
Again,  the  colonies  may  be  small  and  with  entire  margin, 
resembling  those  of  B.  coli. 

Action  on  gelatin 

Much  interest  has  centered  around  the  property  of  gelatin 
liquefaction  of  this  genus.  Hauser  in  his  original  work  laid 
special  emphasis  on  it  and  used  it  as  the  chief  basis  for  his  dis- 
tinction of  types.  Since  then  marked  variations  in  individual 
strains  have  been  observed  by  different  investigators.  Smith 
(1894)  was  able  by  selection  to  transform  a liquefying  Proteus 
vulgaris  into  a non-liquefying  strain.  Herter  and  Broeck  (1911) 
showed  that  a liquefying  strain  of  Proteus  vulgaris  which  had 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


339 


lost  its  liquefying  properties,  but  remained  typical  in  other 
respects,  could  have  the  lost  function  restored  by  passage  through 
a mouse. 

Of  the  73  strains  studied  in  this  investigation,  3 lost  the  prop- 
erty of  liquefying  gelatin  while  in  other  ways  they  remained 
typical.  Two  of  these  organisms  were  old  laboratory  strains 
labeled  Proteus  vulgaris;  the  third  was  isolated  from  putrefying 
meat.  We  were  unable  to  restore  the  liquefying  function  by  a 
single  passage  of  one  of  these  strains  through  a white  rat. 

On  gelatin  plates  of  Proteus  small  colonies  are  noticeable  in 
eighteen  to  twenty-four  hours.  They  show  an  entire  margin  at 
first,  but  as  they  increase  in  size  irregular  spreading  may  occur. 
Liquefaction  soon  takes  place  and  the  colonies  assume  a dew- 
drop  appearance.  Radiating  filaments  extend  from  the  lique- 
fied zone  into  the  surrounding  gelatin.  The  colonies  increase 
in  size  until  the  entire  plate  is  liquefied.  Hauser  employed  5 
per  cent  gelatin,  and  describes  the  occurrence  of  wandering 
ameboid  colonies,  that  is,  irregular  masses  of  cells  which  con- 
stantly underwent  changes  in  form  and  position,  and  sometimes 
separated  from  the  mother  colony.  In  order  to  obtain  colonies 
that  are  at  all  characteristic  gelatin  of  rather  soft  consistency 
is  required.  On  the  usual  10  per  cent  gelatin  the  colonies  are 
often  entire  and  without  distinguishing  marks. 

In  gelatin  stab  cultures  liquefaction  begins  at  the  surface, 
soon  becomes  stratiform  and  eventually  involves  the  entire  tube. 
The  rate  depends  on  the  temperature  and  an  abundance  of  free 
oxygen.  Liquefaction  may  be  completely  inhibited  by  a layer 
of  oil  over  the  surface  of  the  gelatin.  The  oxygen  is  essential 
in  the  production  of  the  proteolytic  enzyme. 

Growth  in  bouillion 

Marked  turbidity  is  rapidly  produced,  reaching  its  maximum 
in  from  three  to  five  days  at  30  to  37  °C.  Young  cultures  usually 
show  no  surface  film,  while  older  tubes  gradually  develop  a thin 
brittle  pellicle  which  is  easily  broken  up.  As  broth  cultures 
present  few  if  any  features  which  are  characteristic  and  of  special 


340 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


interest  no  further  comments  are  necessary.  Nitrite  is  formed 
in  nitrate  broth. 

Action  of  the  genus  Proteus  in  milk 

As  a rule  vigorous  development  occurs  in  milk,  and  a marked 
change  may  be  brought  about  in  the  appearance  of  this  medium 
in  twenty-four  to  thirty-six  hours  at  37 °C.,  the  litmus  being 
reduced  and  coagulation  or  digestion  of  the  casein  taking  place. 
The  rate  of  transformation  varies  with  different  strains,  some 
of  them  completely  digesting  the  casein  in  three  to  five  days. 
On  the  other  hand,  other  strains  appear  to  have  lost  this  pro- 
teolytic power  completely.  The  usual  change  observed  in  this 
study  of  73  strains  was  an  initial  alkalinity  which  gradually  be- 
came more  intense  and  was  followed  by  decolorization  of  the 
litmus  and  digestion  of  the  casein.  Some  strains  (3)  showed  slight 
acid  production  at  first.  Casein  was  digested  by  69  strains. 

The  ability  of  organisms  to  digest  casein  was  demonstrated 
definitely  by  growing  them  in  a medium  containing,  besides  0.5 
per  cent  meat  extract  and  0.5  per  cent  sodium  chloride,  0.2  per 
cent  of  purified  casein,  and  observing  the  loss  of  the  protein  by 
means  of  the  biuret  method  of  Vernon  (1903),  or  by  precipitation 
with  acetic  acid. 

Action  on  carbohydrates , glycerol , etc. 

Fermentation  is  limited  to  glucose,  levulose,  galactose,  sucrose 
maltose  and  glycerol.  The  glucose,  levulose,  galactose  and  glyce- 
rol were  attacked  more  or  less  uniformly  by  all  strains,  sucrose 
readily  by  some  and  slowly  by  others,  and  maltose  only  by  some 
of  the  strains.  Fermentation  in  all  cases  comprises  both  acid 
and  gas  production.  The  medium  employed  in  the  fermentation 
experiments  was  plain  sugar-free  broth  to  which  1 per  cent  of 
the  carbohydrate  in  question  was  added.  Other  agents  used 
were  lactose,  inulin,  dulcitol,  mannitol,  sorbitol,  salicin,  raffinose, 
arabinose,  adonitol,  dextrin  and  starch.  The  results  with  these 
were  negative. 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


341 


Glucose 

This  is  one  of  the  most  favorable  sources  of  energy  for  the 
organisms  of  the  Proteus  genus.  Its  presence  in  a medium  con- 
siderably hastens  growth.  From  25  to  30  per  cent  of  gas,  and 
from  2.5  to  3 per  cent  of  acid  in  terms  of  N/20,  with  phenolphthal- 
ein  as  an  indicator,  are  produced.  These  results  agree  with  those 
of  other  investigators. 

Sucrose 

Smith  (1893)  was  the  first  to  show  that  the  action  of  this  group 
on  sucrose  was  practically  the  same  as  on  glucose.  Similar  results 
have  been  obtained  since  by  other  investigators,  though  Glenn 
(1911)  found  several  indifferent  strains  among  his  stock  cultures, 
and  Horowitz  (1916)  reports  a positive  reaction  in  only  7 out  of 
a total  of  24  strains. 

In  the  present  investigation  a variation  in  the  action  of  Proteus 
on  this  sugar  was  noted,  some  strains  producing  the  maximum 
amounts  of  acid  and  gas  in  twenty-four  to  seventy-two  hours, 
while  others  required  twelve  to  fifteen  days.  The  delayed  ac- 
tion of  the  latter  (8  or  9 days)  was  at  first  overlooked,  but  it  was 
observed  that  when  the  period  of  delayed  action  was  passed  the 
fermentation  was  as  pronounced  as  with  the  strains  which  at- 
tacked the  sucrose  immediately.  Of  the  73  strains  studied,  25 
showed  an  immediate,  and  48  a delayed  action.  In  correlating 
these  results  with  the  action  on  other  carbohydrates,  it  soon  be- 
came apparent  that  the  strains  which  fermented  sucrose  readily 
also  fermented  maltose,  while  those  which  showed  delayed  action 
on  sucrose  did  not  attack  the  maltose. 

Maltose 

Maltose  appears  to  be  the  only  carbohydrate  that  is  of  any 
value  as  a means  of  subdividing  the  Proteus  group.  Berthelot  (1914) 
noted  a variation  in  the  action  of  different  strains  on  this  sugar. 
Horowitz  (1916)  found  that  23  out  of  24  strains  fermented  it 
with  the  production  of  acid  and  gas;  and  Stewart  (1917)  observed 
2 out  of  29  having  this  property.  Of  the  73  strains  in  the  pres- 
ent collection,  25  showed  distinct  acid  and  gas  production.  No 


342 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


delayed  action  on  the  sugar  could  be  detected,  as  in  the  case 
of  sucrose. 

Galactose , levulose  and  glycerol 

While  these  agents  are  fermented  by  this  group  the  action  is 
not  so  marked  and  does  not  occur  as  readily  as  with  the  sugars 
just  mentioned.  The  amount  of  gas  produced  may  vary  from 
a mere  bubble  to  20  per  cent,  and  the  acid  from  1 to  2 cc. 

Lactose 

Conflicting  results  have  been  reported.  While  most  investi- 
gators have  claimed  that  lactose  is  not  attacked  by  the  Proteus 
group,  others  have  observed  fermentation  with  acid  and  gas  pro- 
duction. In  the  light  of  our  own  experiments  these  conflicting 
results  may  be  explained  by  the  presence  of  an  available  carbo- 
hydrate as  an  impurity  in  the  lactose.  When  absolutely  pure 
lactose  was  employed  no  fermentation  could  be  detected  under 
either  aerobic  or  anaerobic  conditions. 

Growth  on  potato 

On  cooked  potato  prepared  in  the  usual  way  very  luxuriant 
growth  is  produced.  It  appears  within  twenty-four  hours  along 
the  line  of  inoculation  and  gradually  spreads  over  the  surface 
irregularly.  It  is  of  a butyrous  consistency  and  of  a dirty  brown 
color  which  quickly  diffuses  through  the  potato.  A characteris- 
tic fish  brine  odor  is  produced  in  this  medium. 

Browning  of  lead  acetate  medium 

All  of  the  73  strains  of  Proteus  used  in  this  investigation  caused 
a distinct  browning  of  a medium  consisting  of  0.5  per  cent  ni- 
trate agar,  0.05  to  0.1  per  cent  lead  acetate,  and  0.2  per  cent 
glucose. 

Hemolytic  action 

This  genus  is  unable  to  hemolyze  red  blood  cells.  Different 
strains  were  tested  both  in  suspensions  of  washed  erythrocytes 
and  on  plates  of  sterile  blood  agar. 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


343 


Growth  in  synthetic  media 

Development  in  Uschinsky  and  similar  synthetic  media  is 
limited.  It  becomes  more  marked,  however,  when  glucose  is 
substituted  for  glycerol  in  the  medium.  In  the  phthalate  medium 
of  Clark  and  Lubs  (1917)  growth  is  likewise  limited. 

Chromogenesis 

With  the  exception  of  a few  investigators  (Ward,  1899,  and 
Jordan,  1903)  the  Proteus  group  is  considered  as  non-pigment 
producing.  In  the  present  work  no  color  production  was  noted 
in  any  of  the  media  except  the  brownish  growth  on  potato  and 
the  gradual  browning  of  the  potato  itself. 

Changes  in  hydrogen  ion  concentration 

In  plain  bouillon  prepared  from  Liebig’s  beef  extract  and  Witte’s 
peptone  no  change  in  titratable  acidity  was  noted,  while  hydro- 
gen ion  determination  by  the  newer  colorimetric  method  showed 
slight  alkali  production.  In  plain  bouillon  containing  an  avail- 
able carbohydrate  sufficient  acid  is  produced  to  bring  the  H 
ion  concentration  to  about  5 on  the  colorimetric  scale.  Similar 
results  were  obtained  in  the  special  peptone  medium  of  Clark 
and  Lubs  (1917).  Little  acid  production  occurs,  however,  in  their 
phthalate  medium  owing  to  the  limited  growth  of  the  organisms. 

Indol  production 

Indol  production  by  this  genus  has  been  pointed  out  by  many 
investigators.  Variations  in  this  property  have  been  noticed  also. 
Steensma  (1906)  studied  several  strains  which  failed  to  produce 
indol.  Van  Loghem  and  Van  Loghem-Pouw  (1912)  made  two 
subdivisions  out  of  the  strains  under  observation,  namely  B. 
proteus-anindologenes  and  B.  proteus-indologenes.  Berthelot 
(1914)  found  that  24  out  of  a total  of  61  strains  formed  indol; 
Horowitz  (1916),  7 out  of  24;  and  Stewart  (1917)  1 out  of  his 
collection  of  29. 


344 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


In  the  present  work  results  were  obtained  which  varied  with 
the  methods  employed.  Dunham’s  solution,  sugar-free  broth, 
and  a 1 per  cent  solution  of  predigested  casein  were  used.  Both 
the  Salkowski  and  the  Ehrlich  aldehyde  method  were  employed. 
Of  the  73  strains  all  gave  a positive  reaction  with  the  sulphuric 
acid  and  nitrite  test  of  Salkowski,  while  46  gave  a reddish  color 
on  the  addition  of  the  acid  alone.  With  the  Ehrlich  method  33 
of  the  73  strains  gave  a strongly  positive,  36  a slightly  positive 
and  4 a negative  reaction.  These  variations  were  obtained  in 
each  of  the  3 media. 

Hydrogen  sulphide  and  mercaptan 

All  of  the  strains  formed  hydrogen  sulphide  in  appreciable 
amounts*  On  the  other  hand,  little  if  any  mercaptan  could 
be  detected.  Mercaptan  production  has  been  the  subject  of 
investigation  on  previous  occasions.  It  has  been  assumed  by 
many  that  this  is  a common  product  of  Proteus , because  this 
genus  is  so  constantly  present  in  organic  matter  undergoing 
putrefactive  decomposition,  though  it  is  not  itself  a strictly 
putrefactive  organism.  Rettger  (1906)  found  no  mercaptan 
in  anaerobic  cultures  of  Proteus  vulgaris  in  egg-meat  mixture. 
Herter  and  Broeck  (1911)  also  were  unable  to  detect  it  in  plain 
bouillon  cultures,  even  when  cystin  was  added.  Ward  (1916) 
claims,  however,  that  he  obtained  marked  mercaptan  production 
with  4 different  strains  which  he  grew  in  plain  bouillon. 

Nine  strains  were  tested  for  the  property  of  mercaptan  pro- 
duction by  the  method  formerly  employed  by  Rettger,  and  in- 
volving the  use  of  isa tin-sulphuric  acid  and  of  mercuric  cyanide. 
In  some  instances  a slight  change  in  the  color  of  the  test  solutions 
could  be  detected,  but  as  control  flasks  gave  a similar  change 
in  color,  little,  if  indeed  any,  mercaptan  was  present  in  the  culture 
flasks.  Contamination  of  such  flasks  with  a putrefactive  anaer- 
obe, however,  soon  resulted  in  abundant  mercaptan  production. 

Putrefaction 

The  experiments  of  Hauser  (1885),  Emmerling  (1896)  and 
others,  demonstrating  putrefactive  changes  in  what  appeared 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


345 


to  be  pure  cultures  of  Proteus  organisms,  as  well  as  the  frequent 
assertions  that  members  of  the  Proteus  group  are  always  present 
in  organic  matter  that  is  undergoing  putrefaction,  has  led  to 
the  assumption  that  this  group  has  distinct  putrefactive  prop- 
erties. Rettger  and  Newell  (1912)  have  shown  more  recently 
that  no  decomposition  of  protein  material  takes  place  under 
anaerobic  conditions  when  pure  cultures  of  Proteus  are  used. 
Similar  experiments  were  conducted  in  the  present  investigation, 
and  the  results  of  Rettger  and  Newell  corroborated.  No  changes 
in  the  character  of  protein  material  could  be  brought  about  by  pure 
cultures  of  Proteus  vulgaris  in  the  absence  of  atmospheric  oxygen, 
whether  in  milk,  egg-meat  mixture,  or  other  protein-containing 
medium.  There  was  no  reduction  in  the  volume  of  the  solid 
matter  in  the  egg-meat  medium,  nor  could  any  of  the  foul  smell- 
ing products  of  putrefaction  be  detected.  Furthermore,  there 
was  very  little,  if  indeed  any  mercaptan  present  in  the  medium. 
Under  aerobic  conditions,  however,  the.  ordinary  non-putref ac- 
tive products  of  protein  decomposition  are  produced. 

Agglutination 

Several  attempts  have  been  made  in  the  past  to  employ  agglu- 
tination as  a basis  for  subdividing  the  Proteus  group.  Cantu 
(1911)  showed  that  the  blood  serum  of  animals  which  had  been 
injected  with  heated  suspensions  of  these  organisms  had  ag- 
glutinating properties  which,  barring  some  exceptions,  were 
specific  for  the  strains  injected.  He  concluded  that  this  method 
can  not  be  employed  for  subdividing  different  strains.  Van 
Loghem  and  Van  Loghem-Pouw  (1912)  claimed  that  indol- 
producing  strains  could  be  distinguished  from  those  which  do 
not  form  indol,  by  their  agglutination  properties.  Horowitz 
(1916)  obtained  cross  agglutinations  among  homologous  strains, 
and  thereby  was  able  to  split  the  Proteus  group  into  5 subdi- 
visions, the  members  of  each  having  specific  properties,  as  re- 
garded indol  production  and  carbohydrate  fermentation. 

In  the  present  work  several  rabbits  were  immunized  against 
specific  strains  of  Proteus  vulgaris  and  Proteus  mirabilis.  Killed 


346 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


suspensions  were  injected  at  first,  followed  by  at  least  one  or 
two  suspensions  of  living  organisms  grown  on  slant  agar  and 
washed  off  with  saline  solution.  After  each  injection  the  animals 
showed  some  loss  in  weight  which  was  very  soon  regained.  At 
the  site  of  inoculation  a large  abscess  was  formed  which  dis- 
appeared only  after  several  months.  The  production  of  agglu- 
tinins could  be  demonstrated  very  soon  after  the  first  injection. 
After  the  last  injection  agglutination  in  as  high  as  1 : 100,000 
dilution  took  place. 

The  different  strains  of  Proteus  were  tested  by  the  macro- 
scopic method  in  dilutions  of  1:50,  1 : 100,  1 : 500,  1 : 1000,  and 
1 : 5000.  Seven  different  sera  were  prepared  with  as  many  strains 
of  Proteus.  Table  1 shows  the  number  of  strains  agglutinated 
by  each  serum.  With  one  exception,  all  of  the  sera  agglutinated 
other  strains  besides  those  employed  in  their  preparation.  Some 
strains  were  agglutinated  by  more  than  one  serum.  Nineteen 
of  the  strains  used  in  the  agglutination  tests  failed  to  be  agglu- 
tinated by  any  of  the  sera.  It  would  appear,  on  the  whole, 
that  the  Proteus  group  is  more  or  less  heterogeneous,  like  the 
Streptococcus  and  B.  dysenteriae  group.  While  the  agglutination 
method  may  be  of  some  value,  in  identifying  members  of  the 
Proteus  group,  negative  results  do  not  necessarily  exclude  an 
organism  from  this  group. 

Pathogenicity 

The  occurrence  of  the  genus  Proteus , either  in  pure  culture 
or  in  association  with  other  organisms,  in  pathological  conditions, 
has  been  reported  by  various  investigators.  Foa  and  Bonome 
(1889)  isolated  it  from  a case  of  volvulus,  Schnitzler  (1890)  and 
Krogius  (1890)  from  cases  of  cystitis,  Flexner  (1893)  from  a 
patient  having  peritonitis,  and  Reed  (1894)  in  croupous  pneu- 
monia, associated  with  a pneumococcus.  Booker  (1897)  and 
Metchnikoff  (1909)  made  Proteus  isolations  from  cases  of  diar- 
rhea in  children,  Vincent  (1909)  from  typhoid  fever  patients, 
and  Horowitz  (1916)  from  persons  suffering  with  gastro-enteri- 
tis.  Larson  and  Bell  (1915)  recovered  Proteus  organisms  from  a 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


347 


laparotomy  wound,  infected  eye  and  finger,  from  the  heart’s 
blood  of  a fatal  case  of  peritonitis,  and  from  one  of  gangrene 
of  the  lung.  Ward  (1916)  obtained  it  from  supposed  diphtheria 
subjects  and  from  typical  cases  of  atrophic  rhinitis. 

Dudgeon,  Gardner  and  Bantree  (1915)  found  typical  Proteus 
in  5 per  cent  and  atypical  Proteus  in  2 per  cent  of  a total  of  100 
cases  of  war  wounds.  Goadby  (1916)  encountered  Proteus  in  47 
per  cent  of  the  200  wounds  studied  bacteriologically.  Distaso 

TABLE  1 


Number  of  strains  agglutinated  by  each  serum  or  combination  of  sera 


NUMBER  OF  STRAINS 

SERA* 

A 

B 

c 

D 

E 

F 

G 

1 

+ 

0 

0 

0 

0 

0 

0 

1 

+ 

+ 

0 

0 

0 

0 

0 

1 

0 

0 

0 

0 

0 

+ 

0 

8 

+ 

+ 

0 

0 

+ 

0 

0 

3 

0 

+ 

0 

+ 

0 

0 

0 

1 

0 

+ 

+ 

+ 

0 

+ 

0 

1 

0 

0 

+ 

+ 

0 

0 

0 

23 

0 

0 

+ 

+ 

0 

+ 

0 

11 

0 

0 

0 

+ 

0 

0 

0 

3 

0 

0 

0 

+ 

+ 

0 

0 

1 

0 

0 

0 

0 

0 

0 

+ 

19 

0 

0 

0 

0 

0 

0 

0 

Total,  73 

10 

13 

25 

42 

11 

25 

1 

* Sera  A,  B,  C,  D,  E and  F were  prepared  with  stock  strains  of  which  the  first 
five  were  labeled  Proteus  vulgaris  Hauser  and  the  last  Proteus  mirabilis  Hauser. 
Serum  G was  prepared  with  a strain  isolated  by  us  from  putrefied  meat. 


(1916)  found  coliform  organisms  including  Proteus  predominating 
in  the  first  stages  of  wound  infection.  He  suggests  the  use  of 
Proteus  vaccine  along  with  others  in  the  treatment  of  war  wounds. 
Stewart  (1917)  isolated  29  strains  of  the  Proteus  genus  from 
infected  war  wounds,  or  a case  rate  of  24  per  cent. 

While  this  genus  is  ordinarily  regarded  as  non-pathogenic, 
there  is  ample  evidence  to  show  that  it  may  assume  a pathogenic 
role,  and  thus  occupy  a position  analogous  to  the  pyogenic  mi- 
crococci. The  pathogenicity  varies  in  experimental  animals, 


348 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


some  strains  causing  death  in  16  to  24  hours,  while  others  cause 
no  apparent  ill  effects.  For  example,  Ktihnau  (1897)  found  that 
strains  from  several  cases  of  diphtheria,  and  Larson  and  Bell 
(1915)  that  some  strains  of  Proteus  obtained  from  human  lesions, 
were  decidedly  pathogenic  for  rabbits,  guinea-pigs  and  rats.  In 
general  the  virulence  of  a strain  is  shown  by  the  production  of 
local  pathological  conditions  or  by  symptoms  of  intoxication. 

In  the  present  investigation  both  virulent  and  non-virulent 
strains  were  met  with.  One  of  the  most  pathogenic  was  an  old 
stock  culture  of  unknown  origin,  this  indicating  that  virulence 
may  be  mantained  indefinitely. 

Hauser,  in  his  original  work  on  the  Proteus  group,  found 
that  boullion  and  gelatin  cultures  were  toxic  and  produced  fatal 
results  when  injected  into  animals.  Other  investigators  have 
obtained  similar  results.  The  nature  of  the  toxicity  is  not  known, 
although  the  effects  are  apparently  those  of  real  toxemia. 

The  toxicity  of  several  strains  of  the  Proteus  genus  was  dem- 
onstrated by  the  writers  by  injecting  2 cc.  of  saline  suspensions 
from  24-hour  agar  cultures.  Subcutaneous  injections  in  rab- 
bits produced  abscesses  and  inflammatory  conditions  which 
lasted  several  months,  usually  accompanied  by  loss  of  weight, 
weakness  and  lessened  appetite.  In  white  rats  the  results  varied 
with  the  strains,  some  causing  symptoms  of  toxemia  and  killing 
the  animals  in  eighteen  to  twenty-four  hours,  when  injected 
by  the  subcutaneous  route.  Others  caused  no  apparent  ill 
effects  even  when  the  injections  were  intraperitoneal.  One  strain 
caused  the  formation  of  an  abscess  in  one  rabbit,  and  definite  symp- 
toms of  toxemia  and  death  in  another.  In  the  fatal  cases  the 
organisms  could  be  isolated  from  the  blood  and  internal  organs. 
Killed  suspensions  when  injected  into  rabbits  caused  definite 
lesions  at  the  site  of  inoculation. 

Classification  of  species 

Since  Hauser’s  classification  several  investigators  have  at- 
tempted to  group  the  various  strains  of  the  genus  Proteus  on 
properties  other  than  gelatin  liquefaction.  Ford  (1901)  defines 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


349 


the  Proteus  group  as  consisting  of  alkali-producing  non-chromo- 
genic,  non-sporing  bacilli  capable  of  liquefying  gelatin,  casein  and 
blood  serum.  He  made  a further  division,  on  the  basis  of  motility 
and  carbohydrate  fermentation,  into  six  varieties,  two  of  which 
fermented  lactose. 

In  his  study  of  bacteria  found  in  river  water,  Jordan  (1903) 
divided  the  Proteus  group  into  two  subdivisions,  namely  the 
Proteus  vulgaris  type  and  Proteus  varieties.  The  first  of  these 
he  described  as  always  fermenting  glucose  and  sucrose,  with  gas 
production,  but  never  lactose;  liquefying  gelatin,  casein  and 
blood  serum,  and  curdling  milk,  with  acid  production.  The 
second  subdivision  differed  from  the  first  mainly  in  its  proteo- 
lytic action.  Cantu  (1911)  in  a study  of  184  strains  isolated  from 
various  sources  was  unable  to  subdivide  them.  Van  Loghem  and 
Van  Loghem-Pouw  (1912)  were  able  to  divide  a series  of  strains 
obtained  mostly  from  intestinal  contents  into  two  groups  on 
the  basis  of  their  indol-producing  function.  The  strains  belong- 
ing to  one  or  the  other  group  were  similar  in  their  agglutinating 
properties.  Horowitz  (1916)  divided  24  strains  into  5 subgroups, 
on  the  basis  of  agglutination.  Stewart  (1917)  found  27  strains 
isolated  from  war  wounds  to  differ  in  their  action  on  maltose 
and  litmus,  and  in  their  motility  and  idol  production. 

The  present  investigation  has  shown  that  attempts  of  others 
to  divide  the  Proteus  group  into  two  or  more  subdivisions  are 
unsound.  The  classification  of  Hauser  on  the  basis  of  gela- 
tin liquefaction  is  of  little  value,  since  this  property  is  too 
irregular  and  inconsistent.  In  their  agglutination  power  the 
members  of  the  Proteus  genus  are  heterogeneous  in  character, 
so  that  no  distinct  separation  into  species  is  possible  on  this 
basis.  Indol  production  is  also  very  unsatisfactory  as  a distin- 
guishing character.  The  only  property  which  appears  to  us 
to  be  of  value  in  making  subdivisions  of  the  genus  Proteus 
is  that  of  carbohydrate  fermentation.  Several  investigators 
have  noted  a difference  in  the  action  of  individual  strains  on 
maltose.  Of  the  73  strains  employed  by  us  25  fermented  this 
sugar,  while  the  remaining  48  failed  to  do  so.  A definite  cor- 
relation existed  between  the  property  of  attacking  maltose  and 


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350 


JOHN  J.  WENNER  AND  LEO  F.  RETTGER 


the  rapidity  with  which  sucrose  was  fermented  with  gas  produc- 
tion. All  of  the  strains  which  fermented  maltose,  with  both 
acid  and  gas  production,  also  fermented  sucrose  readily,  while 
all  of  those  which  failed  to  attack  maltose  showed  a delayed 
action  on  sucrose  and  brought  about  visible  acid  and  gas  pro- 
duction only  after  the  expiration  of  eight  to  nine  days. 

While  no  other  property  could  be  correlated  with  this  action 
on  the  sugar,  it  lends  itself  as  a definite  basis  for  dividing  the 
Proteus  genus  into  two  species,  the  one  fermenting  maltose  with 
acid  and  gas  production,  and  the  other  being  unable  to  attack 
this  disaccharide.  For  the  former  the  name  Proteus  vulgaris 
may  be  retained,  while  for  the  other  Proteus  mirabilis  is  here 
suggested.  By  retaining  these  names  the  nomenclature  would 
be  simplified.  The  differentiating  characters  of  Hauser  must 
be  set  aside,  however,  in  order  to  avoid  confusion. 

GENUS  ZOPFIUS 

Under  this  genus  the  types  formerly  known  as  B.  zopfii  and 
Proteus  zenkeri  will  be  described.  Very  few  strains  of  these 
organisms  are  kept  in  stock,  as  only  4 strains  of  Proteus  zenkeri 
and  5 strains  of  B.  zopfii  could  be  obtained  by  a canvass  of  40 
bacteriological  laboratories.  To  these  9 strains  one  was  added 
which  we  were  able  to  isolate  from  putrefied  meat.  All  of  these 
strains  were  practically  identical. 

The  individual  cells  are  rod-shaped,  usually  about  0.8m  by  3.5m 
in  size,  have  somewhat  rounded  ends,  and  in  young  cultures  occur 
in  long  evenly-curved  chains.  They  stain  well  and  are  Gram- 
positive. The  organisms  are  motile,  having  peritrichous  flagella, 
but  do  not  form  spores  or  capsules.  They  are  facultative 
anaerobes  and  grow  well  on  the  surface  or  directly  beneath 
the  surface  of  agar  apd  gelatin.  In  gelatin  stab  tubes  an  arbores- 
cent growth  results  which  is  most  luxuriant  at  the  top  of  the  stab. 
In  plain  bouillon  growth  is  slow  and  moderate,  while  in  litmus 
milk  it  is  very  scant  and  produces  no  visible  change.  Gelatin 
is  not  liquefied,  and  none  of  the  carbohydrates  are  attacked.  On 
potato  the  growth  is  moderate  with  subsequent  darkening  of 


SYSTEMATIC  STUDY  OF  THE  PROTEUS  GROUP 


351 


the  medium.  The  most  favorable  temperature  for  this  genus 
is  about  25°C.  Good  growth  also  occurs  at  20°  and  at  30°, 
while  at  37  °C.  the  growth  is  very  poor.  No  distinguishable 
odor  was  noted  on  any  of  the  cultures.  Hydrogen  sulfide  was  not 
produced  and  growth  in  egg-meat  medium  was  poor,  resulting  in 
no  visible  changes.  On  slant-agar  and  in  agar  and  gelatin  plates 
a more  or  less  characteristic  spider  web  growth  often  develops, 
but  inoculations  in  the  condensation  water  of  slant  agar  do  not 
cause  a spreading  over  the  surface.  A division  of  the  various 
strains  into  species  did  not  seem  possible  on  account  of  the  few 
differentiating  properties  of  these  organisms. 

SUMMARY  AND  CONCLUSIONS 

The  Proteus  group  has  been  known  to  include  various  types 
of  organisms  some  of  which  have  few  common  properties. 

The  types  Proteus  vulgaris  Hauser,  Proteus  mirabilis  Hauser, 
and  B.  proteus  are,  with  a few  exceptions,  identical.  The  genus 
Proteus  should  be  limited  to  organisms  of  this  group. 

Proteus  zenkeri  is  identical  with  B.  zopfii  and  therefore  should 
not  be  grouped  with  the  Proteus  genus  but  rather  with  B.  zopfii , 
the  organisms  of  this  type  forming  a genus  to  be  known  as 
Zopfius. 

The  organism  Proteus  fluorescens  Jaeger  does  not  resemble  the 
Proteus  genus,  but  rather  the  fluorescent  group  (genus  Pseudo- 
monas),  and  should  not  be  known  by  the  name  Proteus. 

The  Proteus  genus  comprises  a large  group  of  organisms  which 
can  be  subdivided  on  the  basis  of  their  action  on  maltose  into 
two  distinct  species.  For  the  species  fermenting  this  sugar  the 
name  Proteus  vulgaris  is  suggested,  and  for  the  species  failing 
to  attack  it  the  name  Proteus  mirabilis.  The  genus  cannot  be 
subdivided  satisfactorily  on  the  basis  of  proteolytic  action,  indol 
production,  or  agglutinating  properties. 


352 


JOHN  J.  WENNEK  AND  LEO  F.  RETTGER 


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